Crosslinked porous skinless particles of PVC resin

ABSTRACT

Porous particles of crosslinked PVC are disclosed. The particles are skinless and have a fast powder mix time. Processes to produce the novel particles are also disclosed.

This is a division of application Ser. No. 038,087, filed Apr. 14, 1987,now U.S. Pat. No. 4,742,085, issued May 3, 1988.

BACKGROUND OF THE INVENTION

Polyvinyl chloride resins when calendered or extruded give productswhich are very smooth and thus have a glossy finish. For many end usesthis glossy finish is desirable, such as packaging films and clearcontainers. When a rough or dull finish, which is often referred to as amatte finish, is required, it has been suggested that crosslinking thePVC resin would give such a surface. Some end users find the mattefinish desirable for their products. Crosslinking the PVC resin makesthe resin more rubbery thus resulting in the resin being capable ofgiving a matte finish. Crosslinked resins can also offer advantages inother properties such as wear resistance.

Many applications where crosslinked resins would be desirable requirethat the resin be mixed with large amounts of plasticizers. PVC resinsnormally have porosity which allows the resins to absorb plasticizers.Crosslinking a resin detrimentally effects the ability of a resin toabsorb plasticizer quickly. Although the crosslinked resins haveporosity, the plasticizer does not incorporate as quickly as it does ina non-crosslinked resin having the same amount of porosity. This createsa problem in that an extra amount of time is required to incorporate theplasticizer. This time is normally referred to as "powder mix time".

It would be desirable to have a crosslinked PVC resin which wouldquickly absorb plasticizers thereby having a fast powder mix time.

SUMMARY OF THE INVENTION

It is an object of this invention to provide crosslinked PVC resin inparticulate form which are skinless.

It is a further object of this invention to provide crosslinked PVCresins which have short powder mix times.

It is another object of this invention to provide crosslinked PVC resinin particulate form which are non-spherical, highly porous, friable andwhich are skinless.

It is a still further object of this invention to provide processes forproducing the crosslinked resins.

These and other objects will become apparent from the followingdescription of the invention.

A crosslinked PVC resin in particulate form characterized by more than90% by weight of said resin particles having the following features:

(a) said particles are skinless as evidenced by an absence of asubstantially continuous pericellular membrane;

(b) a complex viscosity of from about 0.9×10⁵ poise to about 1000.0×10⁵poise, preferably about 1.0×10⁵ to about 100.0×10⁵, more preferablyabout 4.0×10⁵ to about 60.0×10⁵ ; and

(c) a tan δ less tan 1.0, preferably from about 0.1 to about 0.95, morepreferably from about 0.3 to about 0.7.

It is also preferred that more than 90% of said resin particles have thefollowing features:

(a) a mercury porosity of from about 0.1 cc/g to about 0.8 cc/g,preferably from about 0.3 cc/g to about 0.5 cc/g;

(b) an agglomerated non-spherical shape having a shape factor less thanabout 0.85, preferably less than about 0.83, more preferably less thanabout 0.80;

(c) a weight average particle size of from about 70 microns to about1000 microns, preferably from about 100 microns to about 250 microns;

(d) a friability less than about 2, preferably less than 1, morepreferably 0;

(e) a powder mix time of less than about 400 seconds, preferably lessthan 300 seconds, more preferably less than 250 seconds;

(f) the surface area of said particles is greater than about 20% PVC,preferably greater than about 50%, more preferably greater than about60% as measured by ESCA.

A process is provided for producing the preferred novel particles ofthis invention comprising polymerizing vinyl chloride monomer in thepresence of a crosslinking agent in an agitated aqueous suspensionwherein said aqueous medium contains as the primary dispersant smallamounts of at least one ionic sensitive dispersant capable of thickeningwater and at least one secondary dispersant, wherein an ionic materialis charged to the polymerization medium at from about 1% to 5%conversion of monomer to polymer and the ionic material desorbs asubstantial amount of the ionic sensitive primary dispersant off themonomer droplet, thereby producing a crosslinked skinless, agglomerated,highly porous, friable, PVC resin absent a continuous pericellularmembrane.

Alternate processes are also provided for producing the skinlesscrosslinked PVC particles of this invention.

The resins of this invention, even though highly crosslinked,unexpectedly have short powder mix times and are able to incorporatelarge amounts of plasticizer quickly.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a semi-log graph showing the range of skinless,crosslinked resins made in Example II (Runs 1-24) and the commerciallyavailable skin type crosslinked resins of Example III (A-D). Complexviscosity is plotted on the Y-axis as 10⁵ poises. The Y-axis is a logscale. The X-axis is tan δ. The numbers indicate the run number ofExample II whereas the letters A-D indicate the corresponding resin ofExample III.

DETAILED DESCRIPTION

Polyvinyl chloride resin as used in this invention means polyvinylchloride homopolymers as well as vinyl chloride polymerized with up to50%, preferably up to 20%, by weight of one or more other vinylidenemonomers having at least one terminal CH₂ ═C< grouping. Suitablecomonomers that may be polymerized with vinyl chloride are esters ofacrylic acid, for example, methyl acrylate, ethyl acrylate, butylacrylate, octyl acrylate, cyanoethyl acrylate, and the like; vinylacetate; esters of methacrylic acid, such as methyl methacrylate, ethylmethacrylate, butyl methacrylate, and the like; styrene and styrenederivatives including α-methyl styrene, vinyl toluene, chlorostyrene;vinyl naphthalene; diolefins including butadiene, isoprene, chloroprene,and the like; and mixtures of any of these types of monomers and othervinylidene monomers copolymerizable therewith; and other vinylidenemonomers of the types known to those skilled in the art. The amount ofcomonomer that can be polymerized with vinyl chloride is a function ofthe choice of comonomer, as is well understood by those skilled in theart. Preferably, the polyvinyl chloride polymers of this invention arepolyvinyl chloride homopolymers. The term polyvinyl chloride homopolymeras used in this specification includes the polymerized vinyl chloride aswell as the small amount of crosslinking agents. Technically, thecrosslinked resins of this invention will always be copolymers, becausethe crosslinking agent copolymerizes with the vinyl chloride. However,the amount of crosslinking agent is so small that in this specificationthis resin having only vinyl chloride and crosslinking agent as monomerswill be referred to as a homopolymer. The invention will be described interms of a polyvinyl chloride homopolymer as the preferred embodiment ofthis invention.

The skinless crosslinked resin particles of this invention may beproduced by any one of many processes such as an agitated aqueoussuspension process, which is the preferred process. They may also beproduced by a mass or bulk polymerization process, where polymerizationoccurs in the substantial absence of water and surfactants. A massprocess is described in U.S. Pat. No. 3,522,227, incorporated herein byreference. The mass process produces PVC which is skinless, since thereare no surfactants present.

In the mass process, vinyl chloride is polymerized in mass (in theabsence of additives except a useful quantity of catalyst) using a twostep process in the first of which agitation of high turbulence is usedand in the second very mild agitation, usually related only to themaintenance of uniform temperature in the reaction mass. In the first,high speed step the polymerization is carried to 7 to 15 percentcompletion, preferably about 10 percent. The vessel contents are thentransferred to the second vessel for completion of the polymerization tothe desired degree of conversion. The first stage is normally referredto as a prepolymerizer. The crosslinking agent would be added in theprepolymerizer vessel. Of course one vessel could be used for the masspolymerization, but two vessels are preferred.

A phase inversion process may also be used to produce the crosslinkedskinless resins of this invention. Such a phase inversion process isdisclosed in U.S. Pat. No. 3,706,722, incorporated herein by reference.In the phase inversion process, the monomer is the continuous phaseduring the early part of the polymerization and after about 10%conversion additional water is added such as to make the water thecontinuous phase and the monomer the discontinuous phase. This processin essence runs a mass type polymerization up to about 10% conversionand then inverts to a suspension type polymerization. The invention willbe described in terms of the preferred aqueous suspension process.

The preferred process used to produce the peferred novel resin particlesof this invention is an agitated aqueous suspension process. In theprocess, water is the polymerization medium and a vinyl monomer to waterratio in the range of about 1.0:1.0 to 1.0:10.0 is satisfactory.Preferably, a ratio in the range of about 1.0:1.0 to 1.0:4.0 isemployed.

An important feature of the process to prepare the preferred resinparticles of this invention is the dispersant system that is employed inthe polymerization reaction for the purpose of stabilizing the dispersedmonomer droplets. A colloidal unstable system will result in what isknown as a solid charge, that is, the monomer droplets will agglomerateinto large chunks which are unsuitable for use in normal PVCapplications. A dispersant system which will not allow any agglomerationof monomer droplets will result in spherical particles. Such a processto produce spherical particles is described in U.S. Pat. No. 4,603,151.To obtain the preferred agglomerated skinless particle of this inventionrequires a delicate balance of having a few of the monomer dropletsagglomerate but not excessive agglomeration such as to result inexcessively large particles. An important component of this process isan ion sensitive dispersant which will thicken water. Examples of suchthickeners and how they are used are disclosed in U.S. Pat. No.3,620,988, incorporated herein by reference. The ion sensitivedispersants which will thicken water are usually high molecular weightdispersants or crosslinked dispersants which will thicken water atconcentrations of less than 2% in water, preferably less than 0.2%, andmore preferably less than 0.1% concentration in water. Suitable ionsensitive thickening dispersants include crosslinked polyacrylic acidpolymers, crosslinked ethylene malic anhydride polymers, high molecularweight uncrosslinked polyacrylic acid polymers and ethylene malicanhydride polymers, and the like. The invention will be explained inconnection with a substantially unneutralized crosslinked interpolymer.

A suitable ion sensitive thickener is a substantially unneutralizedcrosslinked interpolymer of one or more carboxylic acid monomers with apolyunsaturated compound having a plurality of terminally unsaturatedpolymerizable groups, for example, a crosslinked polyacrylic acidpolymer. The crosslinking is responsible for making the polyacrylic acidpolymer incapable of forming a true solution in water. In this regard,these polyacrylic acid polymers are classified as being substantiallyinsoluble in water. Nevertheless, the structure of the interpolymer mustbe such that it has enough affinity for water to swell appreciably in anaqueous medium, thus thickening the water phase, but not to the extentthat it cannot be agitated rapidly. Interpolymers that have little or noaffinity for water and do not swell to any measurable degree, are notsuitable for the purposes of the present invention.

With respect to the crosslinked polymeric dispersants used in making theresin of the invention, the carboxylic acid monomers utilizable inpreparing the same are those which contain at least one activecarbon-to-carbon double bond in the α,β-position with respect to acarboxyl group such as ##STR1## wherein R' is hydrogen or a --COOHgroup, and each of R" and R"' is a hydrogen or a monovalent substituentgroup which is linked to one of the doubly bonded carbon atoms.Carboxylic acids within this definition include acids, such as acrylicacid, wherein the double bond is terminal such as ##STR2## or thedicarboxylic acids such as maleic acid and other anhydrides of thegeneral structure ##STR3## wherein R and R' are monovalent substituentgroups and especially those selected from the group consisting ofhydrogen and halogen groups and alkyl, aryl, alkaryl, aralkyl, andcycloaliphatic radicals.

Included within the class of carboxylic acids, shown by generic formula(1) above, are widely divergent materials, such as the acrylic acids,such as acrylic acid itself, methacrylic acid, ethacrylic acid, α- andβ-chloro and bromo-acrylic acids, crotonic acid, maleic acid, itaconicacid, and many others.

Polymerizable carboxylic anhydrides include any of the anhydrides of theabove acids, including mixed anhydrides, and those shown by genericformula (3) above, including maleic anhydride, and others. In manycases, it is preferred to copolymerize an anhydride monomer with acomonomer, such as methyl vinyl ether, styrene, ethylene, and the like.

It is preferred to employ polymeric dispersants which are derived frompolymers produced by the polymerization of the α,β-monoolefinicallyunsaturated carboxylic acids. The preferred carboxylic acids are thosederived from the acrylic acids and α-substituted acrylic acids havingthe general formula ##STR4## wherein R is a monovalent substituentselected from the group consisting of hydrogen, halogen, hydroxyl,carboxyl, amide, ester, lactone, and lactam.

The most preferred polymeric dispersants are those prepared from thelightly crosslinked interpolymers of acrylic acid. These dispersants arethe most effective.

The crosslinking agents which may be employed with any of the carboxylicmonomers, or mixtures thereof, may be any compound, not necessarilymonomeric in nature, containing two or more terminal polymerizable CH₂═C< groups per molecule. Examples of this class of materials includepolyunsaturated-hydrocarbons, -polyethers, -polyesters. -nitriles,-acids, -acid anhydrides, -ketones, -alcohols and polyunsaturatedcompounds of this class incorporating one or more of these and otherfunctional groups. Specifically, there may be utilized divinyl benzene,divinyl naphthalene, low-molecular weight and soluble polymerizeddienes, such as polybutadiene and other soluble homopolymers of openchain aliphatic conjugated dienes, which soluble polymers do not containany appreciable number of conjugated double bonds, and otherpolyunsaturated hydrocarbons; polyunsaturated esters, ester-amides andother ester derivatives, such as ethylene glycol diacrylate, ethyleneglycol dimethacrylate, allyl acrylate, methylene bisacrylamide,methylene bismethacrylamide, triacrylyl triazine, hexallyl trimethylenetrisulfone, and many others; polyunsaturated ethers, such as divinylether, diallyl ether, dimethyl allyl ether, diallyl ethylene glycolether, diallyl, triallyl and other polyallyl ethers of glycerol,butene-1,2-diol, 1-phenyl-1,2,3-propanetriol, the polyallyl, -vinyl and-crotyl polyethers containing from two to seven or more of these orother alkenyl ether groupings per molecule and made from polyhydricalcohols, such as the carbohydrate sugars, and the so-called "sugaralcohols" , including erythritol, pentaerythritol, arabitol, iditol,mannitol, sorbitol, inositol, raffinose, glucose, sucrose, and manyothers, and other polyhydroxy carbohydrate derivatives, thecorresponding polyalkenyl silanes, such as the vinyl and allyl silanes,and others. Of this large class of crosslinking agents, the polyalkenylpolyethers of the carbohydrate sugars, sugar alcohols and otherpolyhydroxy carbohydrate type derivatives containing from two to sevenalkenyl ether groups per molecule are particularly useful. Suchmaterials are easily prepared by a Williamson-type synthesis involvingthe reaction of an alkenyl halide, such as allyl chloride, allylbromide, methallyl chloride, crotyl chloride, and the like, with astrongly alkaline solution of one or more of the poly-hydroxycarbohydrate derivatives.

In the monomeric mixture, for making the crosslinked polymers employedas primary dispersants in the suspension polymerization process used inthis invention, the two essential monomeric materials should be presentin certain proportions, although the exact proportions will varyconsiderably depending on the characteristics desired in the polymer.Small amounts of the polyalkenyl polyether copolymerize quite readilywith carboxylic monomers and the crosslinking effect of the polyalkenylpolyether on the carboxylic monomer is so strong that as little as 0.1%by weight thereof, based on the weight of the total mixture, produces agreat reduction in the water and solvent-solubility of the resultingcrosslinked polymer. When 0.1% to 4.0%, more preferably 0.20% to 2.5%,by weight of the polyether is utilized, water-insoluble polymers areobtained, especially with acrylic acids, which are extremely watersensitive. Useful dispersants are also obtained when 0.1% to 6.0%, andpreferably 0.2% to 5%, of the polyether is copolymerized with maleicanhydride. In the dual copolymer, or two-compound interpolymer, thismeans that the remainder of the monomeric mixture will be the carboxylicmonomer.

The monomeric proportions employed in the production of multi-componentinterpolymers may vary in a somewhat similar manner. However, it isgenerally desirable to utilize as much of the carboxylic monomer ormonomers and as little of the other monomeric constituents as isconsistent with the desired water-insolubility and other properties. Inthese interpolymers, therefore, the carboxylic monomer or monomersshould never be less than 25%, and preferably not less than 40%, byweight of the total monomeric mixture. Multicomponent interpolymers maybe made from monomeric mixtures comprising from 25% to 95% of acarboxylic monomer, such as acrylic acid, 0.1% to 30% of a polyalkenylpolyether, such as a polyallyl polyether of sucrose, and 5.0% to 74.9%of an additional monomer or monomers. Preferred multi-componentinterpolymers are the tripolymers resulting from the polymerization ofmonomeric mixtures containing, respectively, from 40% to 95% by weightof acrylic acid, 0.20% to 2.5% by weight of polyallyl polyether, such asthat of sucrose, and 4% to 59% of an additional monomer or monomers,such as maleic anhydride, N-methyl acrylamide, methyl vinyl ether, ethylvinyl ether, n-butyl vinyl ether, and the like, and mixtures of maleicanhydride, a vinyl alkyl ether, such as vinyl methyl ether, and apolyallyl polyether, in which the sum of the moles of vinyl ether andpolyallyl polyether is substantially equivalent to the molar quantity ofmaleic anhydride present. It should be borne in mind that in the aboveproportions, if a maximum amount of two of the monomers are utilized,that somewhat less than maximum amounts of the other monomers must beutilized.

Suitable for use as additional monomers in the production ofmulti-component interpolymers are monoolefinic vinylidene monomerscontaining one terminal CH₂ ═C< group, such as styrene, the chloro andethoxy-styrenes, etc., acrylamide, N-methyl-acrylamide, N,N-dimethylacrylamide, acrylonitrile, methacrylonitrile, methyl acrylate, ethylacrylate, 2-ethylhexylacrylate, methyl methacrylate, vinyl acetate,vinyl benzoate, vinyl pyridine, vinyl chloride, vinylidene chloride,vinylidene chlorobromide, vinyl carbazole, vinyl pyrrolidone, methylvinyl ether, ethyl vinyl ether, n-butyl vinyl ether, methyl vinylketone, ethylene, isobutylene, dimethyl maleate, diethyl maleate, andmany others. In addition to the above monoolefinic monomers, many of thedivinyl dialkenyl or other polyfunctional esters, amides, ethers,ketones, and the like, may be used in the production of multi-componentinterpolymers, especially those polyfunctional monomers which nominallyfunction as crosslinking or insolubilizing monomers but which are easilysaponified and hydrolyzed to additional hydroxyl, carboxyl and otherhydrophilic groups. For example, an interpolymer of acrylic acid anddivinyl ether is insoluble in water but upon standing gradually goesinto solution probably due to hydrolysis and breaking of divinyl ethercrosslinks. The presence of strong alkali or acid speeds dissolution.Spectroscopic analysis confirms the presence in the polymers ofnon-carboxylic hydroxyls. Similarly, diesters, such as diallyl maleate,ethylene glycol dimethacrylate, acrylic anhydride, betaallyloxyacrylate, and many others, are readily saponified or hydrolyzed byalkali or acid with the introduction of additional hydroxyl and/orcarboxyl groups. Of the additional monomers, N-methyl acrylamide, methylvinyl ether, ethyl vinyl ether and divinyl ether have been foundparticularly useful in the production of the substantially unneutralizedcrosslinked interpolymers for use as ion sensitive dispersants in thesuspension polymerization of vinyl monomers.

The amount of the water-insoluble substantially unneutralizedcrosslinked interpolymer useful as an ion sensitive dispersant, in theprocess of making the novel resins of this invention will vary in therange of about 0.01 parts by weight to about 0.1 parts by weight, basedon 100 parts by weight of the monomer or monomers being polymerized.Preferably, the amount used will be in the range of about 0.02 parts byweight to about 0.06 parts by weight per 100 parts by weight of monomeror monomers being polymerized

In the process to make the novel preferred resins of this invention,other secondary dispersants are preferably employed, along with the ionsensitive dispersant. Dispersants which tend to form a skin on the resinparticles such as methyl cellulose and high hydrolysis (above 70%)polyvinyl acetate should be avoided. The secondary dispersants should bemonomer soluble and not fully soluble in water. For PVA secondarydispersants, the higher the % hydrolysis, the more water soluble thedispersant. For example, 30% hydrolyzed PVA is monomer soluble and notwater soluble, 55% hydrolyzed PVA is very soluble in the vinyl monomerbut is also partially soluble in water. 72.5% hydrolyzed PVA is fullywater soluble and therefore not acceptable. The fully water solubledispersants will form a skin on the polymer particle. Oil-solublenon-polyethylene oxide containing secondary dispersants are suitable foruse in this invention. Suitable non-polyethylene oxide containingsecondary dispersants are those compounds from the sorbitan ester familyor the glycerol ester or polyglycerol ester families, as well as the lowhydrolysis (less than 70%, preferably less than 60%, and more preferablyless than about 55%) polyvinyl acetates, which do not containpolyethylene oxide segments. As examples of such dispersants, there maybe named sorbitan trioleate, sorbitan tri-stearate, sorbitan monooleate,sorbitan monopalmitate, glycerol monooleate, glycerol monostearate,triglycerol monooleate, 50% hydrolyzed polyvinyl acetate, and the like.A mixture of more than one of these dispersants may be used. Thefunction of the secondary dispersants is to increase the porosity of thepolymer particles and to increase the colloidal stability of thepolymerization mixture. The non-polyethylene oxide containing dispersantis used at a level of from about 0.005 part by weight to about 1.0 partby weight per 100 parts by weight of monomer, preferably from about 0.1part by weight to about 0.4 part by weight per 100 parts by weight ofmonomer. More than one secondary dispersant may be used in thisinvention to achieve the secondary dispersant level.

The polymerization is initiated with a free radical catalyst. Themonomer-soluble or oil-soluble catalysts that may be used in thepolymerization process of this invention are the alkanoyl, aroyl,alkaraoyl, and aralkanoyl diperoxides and monohydroperoxides, azocompounds, peroxy ester, percarbonates, and other free radical typecatalysts. As examples of such catalysts, there may be named benzoylperoxide, lauryl peroxide, diacetyl peroxide, cumene hydroperoxides,methyl ethyl ketone peroxide, diisopropylbenzene hydroperoxide,2,4-dichlorobenzoyl peroxide, naphthoyl peroxide, t-butyl perbenzoate,di-t-butyl perphthalate, isopropyl percarbonate, acetyl cyclohexanesulfonyl peroxide, disecondary butyl peroxydicarbonate, 5-butylperoxyneodecanoate, di-normal propyl peroxydicarbonate, azo-bisisobutyronitrile, α,α'-azodiisobutyrate, 2,2'-azo-bis-(2,4-dimethylvaleronitrile), and many others. The particular free radical catalystemployed will depend upon the monomeric material(s) being polymerized,the molecular weight and color requirements of the polymer, thetemperature of polymerization, etc. Insofar as the amount of catalystemployed is concerned, it has been found that an amount in the range ofabout 0.005 parts by weight to about 1.00 parts by weight, based on 100parts by weight of the monomer or monomers being polymerized, issatisfactory. However, it is preferred to employ an amount of catalystin the range of about 0.01 part by weight to about 0.20 part by weightbased on 100 parts by weight of monomer(s).

The preferred suspension polymerization process of this invention may becarried out at any temperature which is normal for the monomericmaterial to be polymerized. Preferably, a temperature in the range ofabout 0° C. to about 100° C. is employed, more preferably from about 40°C. to about 80° C. In order to facilitate temperature control during thepolymerization process, the reaction medium is kept in contact withcooling surfaces cooled by water, brine, evaporation, etc. This isaccomplished by employing a jacketed polymerization reactor wherein thecooling materials are circulated through the jacket throughout thepolymerization reaction. This cooling is necessary since most all of thepolymerization reactions are exothermic in nature. It is understood, ofcourse, that a heating medium can be circulated through the jacket, ifnecessary.

The preferred process to produce resins of this invention involves usingan ionic material to desorb the primary dispersant off the resin.Suitable ionic materials are bases which will neutralize the polyacrylicacid primary dispersant and form a salt. Preferably, the ionic materialis a monovalent inorganic or organic base such as amines, sodiumhydroxide, ammonium hydroxide, potassium hydroxide, lithium hydroxide,and the like. The most preferred ionic material is sodium hydroxide.Divalent and trivalent materials can crosslink the polyacrylic acidprimary dispersant and would therefore not normally be chosen as theionic material. The preferred embodiment of this invention will bedescribed in terms of using sodium hydroxide as the ionic material. Theprimary dispersant protects the monomer droplets at the very earlystages of polymerization. Before the primary dispersant can graftpolymerize with the vinyl chloride, NaOH is added to the polymerizationmedium. The ion sensitive primary dispersant will then swell in size anddesorb off the droplet. Protection of the droplet is accomplished afterthis point by the increased size of the primary dispersant. The NaOHmust be added early in the polymerization, usually from 0.5% to 5.0%conversion of monomer to polymer. If the NaOH is added at the beginningor before about 0.5% conversion, the primary dispersant will be desorbedoff the droplet too early and could result in an unstable suspension.Preferably the NaOH is added at from 1% to 3% conversion, morepreferably 1% to 2% conversion. Since the primary dispersant is desorbedfrom the droplet and polymerization is continued without a primarydispersant on the particle, the resulting resin is essentiallyskin-free. Of course, some primary dispersant can become attached to theresin particle without departing from this invention but there cannot bea continuous pericellular membrane present as there is in normalsuspension PVC resin.

The amount of NaOH typically added is an amount sufficient to raise thepH about 0.5 to 1.0 point. Usually the amount of NaOH needed to desorbthe primary dispersant is from about 0.0010 part by weight to about0.0100 part by weight per 100 parts of monomer. More could be used butit would not serve a useful purpose.

If an ion sensitive dispersant is used which will thicken by loweringpH, then rather than adding NaOH to desorb the dispersant, HCl could beused. The HCl would work in the same fashion as described above andshould be added at similar low conversion levels as described above.

An alternate process to produce the crosslinked skinless resins of thisinvention is to use extremely low levels of the ion sensitive primarydispersant. Levels of from about 0.01 to about 0.03 parts by weight per100 parts by weight of polymerizable monomer should be used in thisalternate method. If these low levels are used, then it is not necessaryto use the NaOH to desorb the primary dispersant from the monomerdroplet. Secondary dispersants at levels described above are used inthis alternate method.

An additional alternate process to produce the resins of this inventioninvolves the use of a combination of dispersants. The combination ofdispersants are non-polyethylene oxide containing secondary dispersantssuch as sorbitan esters, for example sorbitan monooleate andnon-polyethylene oxide containing dispersants such as low hydrolysisPVA, and primary dispersant polyacrylic acid. Sorbitan esters areeffective porosifiers but in amounts greater than 0.1 part they tend tobe highly destabilizing. It was also found that higher levels of about0.2 to 0.4 part of sorbitan ester would prevent the formation of a skinby the primary dispersant. It was also found that low hydrolysis PVA(less than 70%, preferably less than 60%, more preferably less thanabout 55%) in amounts of from about 0.1 to 0.3 part by weight wouldcounteract the destabilizing effect of sorbitan ester. The level ofpolyacrylic acid dispersant used in this additional alternate process togive skinless crosslinked resin will vary depending upon the level ofPVA. For levels of PVA of about 0.3 part, the polyacrylic aciddispersant needs to be less than 0.04 part, whereas for levels of PVA ofabout 0.1, the level of polyacrylic acid dispersant can be higher, suchas about 0.06. As the level of PVA increases, the level of polyacrylicacid dispersant must decrease to obtain a skinless resin. Highhydrolysis PVA's greater than 70% and dispersants such as methylcellulose should be avoided because they will form a skin on the resin.

Reactor Charging Procedure

In the preferred process to produce skinless resins of this invention, acharging procedure similar to the one disclosed in U.S. patentapplication Ser. No. 06/846,163 filed March 31, 1986, incorporatedherein by reference, should be used. The procedure used is what is knownas a one poly floating method. The free radical catalyst is first mixedwith a solvent, such as isopropol alcohol, in the preferred process.This technique of using a catalyst solution and its added benefits arefully disclosed in the above incorporated patent application. Thepolymerization reactor charging procedure is explained in the stepsbelow.

(a) Charge water and ion sensitive primary dispersant(s) capable ofthickening water to the polymerization vessel. The primary dispersant(s)can be added as such but is preferably added as a concentrated mixturewith water. The water and primary dispersant(s) may be premixed beforecharging to the polymerization vessel. The charge water is preferablydemineralized water.

(b) Agitate the water and primary dispersant(s) until an emulsion isformed.

(c) Reduce or stop the agitation such that non-turbulent flow isachieved.

(d) Charge the monomer(s) and crosslinking agent to be polymerized tothe reactor vessel such that said monomer floats on top of theemulsified thickened aqueous layer.

(e) Charge a solution comprising a solvent and the free radical catalystand optionally the secondary dispersant(s) to the reactor. If thesecondary dispersant(s) are not combined with the catalyst solution,then they should have been premixed with the monomer before adding tothe reactor.

(f) Allow the catalyst solution to diffuse through the monomer layer.

(g) Increase the agitation such that the entire polymerization medium isemulsified.

(h) Conduct to polymerization until 1% to 2% conversion is reached, thenadd NaOH to desorb the primary dispersant from the monomer droplet.

(i) Continue the polymerization until the desired degree ofpolymerization is achieved.

An alternate charging method, known as the two poly method, is to firstadd the monomer(s) and crosslinking agent to the reactor together withthe solution containing the catalyst and secondary dispersant(s). Thecatalyst solution could, of course, be premixed with the monomer priorto adding to the reactor vessel, in which case agitation would not benecessary after adding to the reactor. This mixture is then agitatedthoroughly. The thickened water, which had been previously made up bymixing the ion sensitive thickening primary dispersant(s) with water, ischarged into the bottom of the reactor through a bottom entry port.Agitation is then re-started and polymerization conducted as above.

The catalyst could also be charged neat into the water phase containingthe primary dispersant. If this method were used, then the catalystwould not first be premixed with the solvent.

To produce the crosslinked skinless resins of this invention, acrosslinking agent is used. The preferred crosslinking agents are thosematerials which are soluble in the vinyl monomer and the vinyl polymer.The reactivity ratio of the crosslinking agent should be such that itprefers to add to the vinyl monomer rather than to add to itself. Therate constants (k) of the various reactions involved can be expressedas: ##STR5## The monomer reactivity ratio of vinyl monomer (R₁) can beexpressed as

    R.sub.1 =k.sub.11 /k.sub.22

The monomer reactivity ratio of the crosslinking agent (R₂) can beexpressed as

    R.sub.2 =k.sub.22 /k.sub.21

Ideally the product of R₁ and R₂ would be equal to 1 (R₁ ×R₂ =1).

The crosslinking agents should be completely reacted before the normaltermination of the polymerization, so as not to have crosslinkingmonomer present as residual monomer in the vinyl polymer. Vinyl chloridepolymerizations are normally run to a % conversion of monomer to polymerof from about 50% to 90%, preferably from about 65% to about 80%. Theconversions can of course be higher or lower depending on the desiredproperties of the resin.

The crosslinking agents which are suitable to produce the novel resin ofthis invention include, for example, diallyl phthalates such as diallylphthalate, diallyl isophthalate, diallyl terephthalate, etc.; diallylesters of ethylenically unsaturated dibasic acid such as diallylmaleate, diallyl fumarate, diallyl itaconate, etc.; diallyl esters ofsaturated dibasic acid such as diallyl adipate, diallyl azelate, diallylsebacate, etc.; divinyl ethers such as diallyl ether, triallylcyanulate,triallyl isocyanurate, triallyl trimellitate, ethylene glycol divinylether, n-butanediol divinyl ether, octadecan divinyl ether, etc.;di(meth)acryl esters of polyhydric alcohols such as ethylene glycoldimethacrylate, diethylene glycol dimethacrylate, diethylene glycoldiacrylate, triethylene glycol methacrylate, etc.; tri(meth)acryl estersof polyhydric alcohols such as trimethylolpropane trimethacrylate,trimethylolethane trimethacrylate, trimethylolpropane triacrylate,trimethylolmethane triacrylate, tetramethylolmethane triacrylate, etc;polyfunctional compounds such as bismethacryloyloxyethylene phthalate,1,3,5-triacryloylhexahydrotriazine, etc. A mixture of more than onecrosslinking agent may be used. Diallyl phthalate is the most preferredcrosslinker for making the resins of this invention.

The crosslinking agent may be added to the polymerization medium in anymanner known to those skilled in the art; such as premixing with thevinyl monomer before charging, charging directly into the polymerizationmedium or metering into the reaction during the polymerization. Thepreferred method is to first premix the crosslinking agent with thevinyl monomer before charging to the reaction vessel. If a masspolymerization is used to produce the crosslinked skinless resins ofthis invention, then the crosslinking agent should be added in theprepolymerizer.

The amount of crosslinking agent used to make the resins of thisinvention is from about 0.05 part by weight to about 5.0 parts byweight, preferably about 0.15 part to about 1.0 part by weight, morepreferably about 0.25 part to about 0.6 part by weight per 100 parts byweight of vinyl monomer.

The polymer particles produced by the present invention should have anaverage diameter by weight greater than about 70 microns. The particlescould have an average diameter up to 1000 microns but normally, thepolymer particles will have an average diameter by weight less thanabout 300 microns. Preferably, for most end uses, the polymer particleswill have a diameter in the range of about 100 microns to about 250microns, most preferably from about 125 microns to about 200 microns.Resins with an average particle size by weight less than 70 microns tendto be dusty and build up static easily such that they are lessdesirable.

The preferred resin particles of this invention are agglomeratednon-spherical in shape. The preferred agitated aqueous suspensionprocesses described above will give an agglomerated non-spherical resinparticle. A mass process and the phase inversion process of U.S. Pat.No. 3,706,722 both give more spherical shaped resins than does thepreferred agitated aqueous suspension process. A very good method tomeasure the spherical shape of resins is to determine the shape factorby optical procedures. The image of the particle is projected onto aflat surface to provide a two dimensional view. The shape factor of aparticle is determined by inscribing and circumscribing the resinparticles flat image with a circle. The ratio of the diameters of theinscribed circle to the circumscribed circle is the number known as theshape factor.

In the case of a perfect circle, the inscribed and circumscribed circleswould have the same diameter and, therefore, the shape factor would beunity (1.0). The more near the shape factor is to 1.0 the more sphericalthe particle.

The shape factor of the resin particles made by the preferred agitatedaqueous suspension process of this invention is less than about 0.85,preferably less than about 0.83, and more preferably less than about0.80. The shape factor of resin particles made by the mass process andthe phase inversion process are from about 0.87 to about 0.91.

The preferred resin particles made by this invention also have highporosity of from about 0.10 cc/g to about 0.8 cc/g as measured usingmercury porosimeter. Preferably, the mercury porosity is from about 0.30cc/g to about 0.50 cc/g. Porosity is measured according to ASTM D-2873procedure. Sometimes porosity is measured as DOP porosity, which givesresults about 0.02 cc/g higher than mercury porosity values reportedherein for the same resin. When using a mass process, low conversions offrom 35% to 65%, preferably 40% to 50% of monomer to polymer, are usedto achieve high porosity.

The resins of this invention must be skinless. The term skinless as usedin this specification means that the resin does not have a continuouspericellular membrane as does a typical PVC resin. There may bediscontinuous areas or spots of skin on the resin surface but the resinwould still be considered skinless under the meaning used in thisinvention. The term skinless as used herein includes what is normallyreferred to as low-skin.

One method to characterize skinless resins is to determine thecomposition of the surface of the resin particle by use of XPS (ESCA)technique. If a resin was totally skinless, there would not be anyprimary dispersant on the surface. The surface of the resins of thisinvention will have less than 40%, preferably less than 25%, and morepreferably less than 10%, of the primary dispersant, as measured by ESCAtechnique. The surface will consist mainly of PVC and secondarysurfactants (porosifiers).

The resin particles of this invention have a surface composition asmeasured by ESCA greater than about 20% PVC, preferably greater thanabout 50%, more preferably greater than about 60%. This indicates thatthe particles have a significant portion of holes in their skin, wheresaid holes allow the plasticizer to easily pass into and be absorbed bythe particle. ESCA is an acronym that stands for electron spectroscopyfor chemical analysis. The ESCA technique involves irradiating thesample with X-rays from an X-ray tube. The X-rays knock electrons out ofthe atoms that are on the surface of the sample. The energy and numberof these electrons are measured. From that information one can determinewhat elements are present. The depth of analysis of ESCA is about 20 to30 angstroms which is about 5 or 6 monolayers of atoms on the surface ofa sample. One should keep in mind that the ESCA test conducts ananalysis of the surface visible to the ESCA. In a skinless or low skinresin, pores are open to the surface, therefore the X-rays are goinginto the pores and the results reflect an analysis of the bottom of thepore as well as the outermost surface of the resin particle. Thisexplains to a great deal why the ESCA analysis of a skinless resin showsthe secondary dispersant present. The secondary dispersant is believedto be present on the primary particles which are visible when lookinginto the pores.

Another method to determine if a resin is skinless is to look at theresin under magnification or take micro-photographs of resin particlesand observe if a continuous skin or pericellular membrane exists. In amicro-photograph, an observer can see into the internal area of theresin particles of this invention. The high porosity, friable particlesappear like a sponge with many openings in the surface of the resinparticle. These openings allow for fast plasticizer uptake and create afriable particle which is easily broken down into smaller units (primaryparticles).

The resin particles of this invention also have a fast powder mix timeas measured using a torque rheometer according to ASTM D-6373. The resinparticles of this invention have a powder mix time of less than about400 seconds, preferably less than 300 seconds, more preferably less than250 seconds.

The preferred resins of this invention also have good friability. Thefriability value of a resin is an indication of the relative ease withwhich grains break down into agglomerates and finally to primaryparticles. The lower a resin's friability value, the more desirable theresin. High friability values are known to relate to temporary fish-eyesand surface roughness in flexible extrudates. Fish eyes are undesirableareas in a product, such as a film, which are areas of non-uniformity.This is especially important in powder extrusion and high plasticizerapplications. One method to test PVC resin for friability is to place agiven amount of resin in a mortar and grind the resin with a pestle. Thebetter the friability, the easier the resin particles will break apart.The friability is then subjectively graded on a scale of from 0 to 5,with 0 being very friable and equivalent to the best known PVC forfriability. A level of 5 is equivalent to a high quality general purposegrade resin. Values between 0 and 5 are rated as to how they comparewith reference standards which are blends of a 0 value resin and a 5value resin. The resins of this invention have a friability value ofabout 2 or less, preferably they have a friability value of 1 or less,and more preferably they have a friability value of 0.

For reference, make up standards using blends of Geon® 92 (a skinlessspherical PVC resin produced by B. F. Goodrich according to the processof U.S. Pat. No. 3,706,722) and well known for its excellent friabilityand Geon® 30 (a high quality general purpose grade PVC resin with a skinproduced and sold by B. F. Goodrich) as follows:

Reference Standard "0" is a mix of Geon 92: 100 parts and Geon 30: 0parts.

Reference Standard "1" is a mix of Geon 92: 80 parts and Geon 30: 20parts.

Reference Standard "2" is a mix of Geon 92: 60 parts and Geon 30: 40parts.

Reference Standard "3" is a mix of Geon 92: 40 parts and Geon 30: 60parts.

Reference Standard "4" is a mix of Geon 92: 20 parts and Geon 30: 80parts.

Ref2erence Standard "5" is a mix of Geon 92: 0 parts and Geon 30: 100parts.

Compare the friability of the resin tested to the friability of thereference standards. Choose the standard which most closely correspondsto the test resin and report that standard as the friability of the testresin.

The behavior of a PVC resin during compounding (and that of theresulting compound during processing) is controlled by such propertiesas resin particle size, porosity and temperature-shear rate dependentrheology. The rheology or flow behavior of PVC is significantlyinfluenced by resin molecular weight, crystallinity, composition andbranch structures that might be present. The best method ofcharacterizing these molecular properties, especially when branchstructures are present, is to analyze the viscoelastic properties of theresin. The crosslinked resins of this invention may be characterized bytheir viscoelastic properties.

The method used for determining viscoelastic properties of the resins ofthis invention involves subjecting a disk-shape sample to very smalldeformation (less than 1% strain) in a cyclic fashion using aRheometrics Mechanical Spectrometer equipped with oscillating parallelplates. During deformation of the sample, a certain amount of energy islost due to molecular segmental motions. The remaining energy is storedby elastic mechanisms. These two types of behavior are simultaneouslymeasured during testing and are reflected in the magnitudes of the lossmodulus (G") and storage or elastic moldulus (G'). Also measured is thecomplex viscosity (n*), which is analogous to the steady state shearviscosity as might be measured by a capillary rheometer.

Complex viscosity is an indication of molecular weight. Intrinsicviscosity (IV) is normally the method of expressing molecular weight ofa PVC resin. However, with crosslinked resins the resin is notcompletely soluble, thus the IV cannot be accurately determined.Therefore molecular weight of the resins of this invention are expressedas complex viscosity, with the units being poise. The complex viscosityis measured at 210° C. The resins of this invention have a complexviscosity of from about 0.9×10⁵ poise to about 1000.0×10⁵ poise,preferably about 1.0×10⁵ to about 100.0×10⁵, more preferably about4.0×10⁵ to about 60.0×10⁵. In terms of behavior, a complex viscosity of0.9×10⁵ poise corresponds to an IV of from about 0.8, and a complexviscosity of 60.0×10⁵ poise corresponds to an IV of about 1.5.

Another important viscoelastic property of the resins of this inventionis the tan , which is the ratio of the loss modulus (G") to the energystorage modulus (G'). The tan δ can be expressed by the formula:

    Tan δ=G"/G'

Tan δ is an indication of the amount of long chain branching(crosslinking) present in the resin. A PVC homopolymer with nocrosslinking would have a tan δ of about 1.0. As crosslinking occurs,the tan δ gets smaller. The tan δ of the crosslinked resins of thisinvention are less than 1.0, preferably from about 0.1 to about 0.95,more preferably from about 0.3 to about 0.7. The tan δ is measured at210° C.

To further illustrate the present invention, the following specificexamples are given, it being understood that this is merely intended inan illustrative and not a limitative sense. In the examples, all partsand percents are by weight unless otherwise indicated.

EXAMPLE I

This Example is presented to demonstrate a process to produce thecrosslinked skinless resin of this invention. An 1100 gallon reactorequipped with agitation and cooling means was used in this Example. Thefollowing polymerization recipe was used:

    ______________________________________                                        Ingredient           Parts by Wt.                                             ______________________________________                                        Vinyl Chloride       100                                                      Water (demineralized)                                                                              150                                                      Diallyl phthalate    0.260                                                    Polyacrylic Acid Dispersant                                                                        0.025                                                    NaOH                 0.0025                                                   Isopropyl Alcohol    0.120                                                    Low Hydrolysis (55%) PVA                                                                           0.300                                                    2-ethyl Hexyl Peroxydicarbonate                                                                    0.045                                                    Phenolic Shortstop   0.020                                                    ______________________________________                                    

The ingredients were charged according to the two poly method disclosedin this specification. The reaction was conducted at 53° C. The NaOH wascharged as a solution in water after 15 minutes into the reaction (about1% conversion). At 275 minutes the reaction was terminated with thephenolic shortstop. The resin was removed from the reactor, stripped ofresidual monomer and dried to a free flowing powder.

The resin particles were agglomerated, irregular shaped, porous,crosslinked skinless resin particles with the following properties:

    ______________________________________                                        Weight average particle size                                                                        160 microns                                             Mercury porosity      0.407 cc/gm                                             Powder mix time       216 seconds                                             Complex viscosity     20 × 10.sup.5 poise                               Tan δ           0.5                                                     ______________________________________                                    

This example demonstrates a crosslinked skinless resin having a fastpowder mix time, and high porosity. The tan δ indicates a significantamount of crosslinking. This resin when calendered or extruded will givea matte finish.

EXAMPLE II

This Example is presented to show a broad variety of crosslinkedskinless PVC resins with different amounts of crosslinking. The samepolymerization recipe and charging procedure was used as in Example Iexcept the amount of crosslinking agent (diallyl phthalate) andpolymerization temperature. The part level of crosslinking agent isparts per 100 parts vinyl chloride monomer. The following results wereobtained:

                                      TABLE I                                     __________________________________________________________________________               Crosslink                                                                           Complex                  Wt. Avg.                                 Reaction                                                                            Agent Visc. × 10.sup.5                                                                  cc/g   Powder  Particle                            Run No.                                                                            Temp. °C.                                                                    Part Level                                                                          poise Tan δ                                                                       Hg Porosity                                                                          Mix Time-Sec.                                                                         Size-Micron                         __________________________________________________________________________    1    55    2.0   45.00 0.17                                                                              0.71   159     236                                 2    40    0.60  53.00 0.24                                                                              0.35   363     136                                 3    53    0.60  20.00 0.38                                                                              0.75   --      191                                 4    60    0.75  16.00 0.39                                                                              0.44   181     218                                 5    53    0.45  20.70 0.42                                                                              0.42   --      150                                 6    53    0.45  20.20 0.45                                                                              0.38   --      235                                 7    60    0.50  11.00 0.49                                                                              0.45   227     150                                 8    65    0.75  10.90 0.43                                                                              0.38   215     163                                 9    53    0.32  13.00 0.54                                                                              0.41   --      145                                 10   55    0.40  15.30 0.55                                                                              0.31   --      226                                 11   60    0.25  5.40  0.88                                                                              0.41   227     144                                 12     70.5                                                                              0.76  5.90  0.54                                                                              0.31   259     149                                 13   65    0.50  8.05  0.60                                                                              0.36   295     182                                 14   50    0.15  16.00 0.73                                                                              0.41   --      235                                 15   53    0.15  10.60 0.82                                                                              0.39   --      150                                 16   64    0.40  6.30  0.75                                                                              0.32   240     185                                 17   64    0.30  4.45  0.75                                                                              0.31   228     169                                 18   70    0.50  1.90  0.68                                                                              0.78   --      453                                 19   70    0.25  0.92  0.73                                                                              0.46   136     218                                 20   65    0.25  2.38  0.79                                                                              --     --      --                                  21   58    0.20  6.20  0.80                                                                              0.37   225     166                                 22   58    0.15  5.70  0.82                                                                              0.36   256     167                                 23   56    0.15  7.40  0.85                                                                              0.36   --       97                                 24   70    0.75  4.50  0.52                                                                              0.67   --      214                                 __________________________________________________________________________

The complex viscosity and Tan δ are plotted on a semi-log graph andshown as the attached FIGURE. The graph shows the broad range ofcrosslinked resins produced in this Example. The numbers beside thepoint on the graph correspond to the Run No. of this Example II.

EXAMPLE III

This Example is presented to compare commercially available crosslinkedPVC resins which have a skin to the skinless crosslinked resins of thisinvention.

                                      TABLE II                                    __________________________________________________________________________             Complex                 Wt. Average                                  Commercial Skin                                                                        Visc. × 10.sup.5                                                                  Hg Porosity                                                                          Powder Mix                                                                           Particle Size                                Type PVC Resin                                                                         Poise Tan δ                                                                       cc/g   Time - Sec.                                                                          Micron                                       __________________________________________________________________________    A        44.50 0.70                                                                              0.349  448    119                                          B        31.50 0.62                                                                              0.366  556    123                                          C        14.80 0.59                                                                              0.204  477    123                                          D         5.75 0.62                                                                              0.239  829    109                                          __________________________________________________________________________

As can be seen from the above data, the powder mix time is much longerfor the crosslinked resins which have a skin than the powder mix timesof the skinless crosslinked resins of this invention.

The above four competitive skin type crosslinked resins are shown on theFIGURE. The FIGURE is a semi-log graph of complex viscosity vs. Tan δ.The letters A-D beside the point indicate the corresponding resin ofthis Example III.

The resins of this invention have many uses where a matte finish isdesired in a PVC product such as house siding and window cladding. Thecrosslinked resins of this invention may be used as 100% of the PVCrequired in a PVC formulation or they may be blended withnon-crosslinked PVC resins in any proportions to achieve a desiredresult.

I claim:
 1. A crosslinked polyvinyl chloride resin in particulate formcharacterized by greater than about 90% by weight of said resinparticles having the following features:(a) said particles are skinlessas evidenced by an absence of a substantially continuous pericellularmembrane; (b) a complex viscosity of from about 0.9×10⁵ poise to about1000.0×10⁵ poise as measured at 210° C.; (c) a tan δ of less than 1.0 asmeasured at 210° C.; (d) a mercury porosity of from about 0.1 cc/g toabout 0.8 cc/g; (e) a particle size of from about 70 microns to about1000 microns; (f) a friability of less than about 2; (g) a powder mixtime of less than about 400 seconds; (h) a shape factor less than about0.85; and (i) wherein greater than about 20% of the area of the surfaceof said particles is PVC as measured by ESCA.
 2. A resin of claim 1wherein said resin is a PVC homopolymer.
 3. A resin of claim 2 whereinsaid tan δ is from about 0.3 to about 0.7.
 4. A resin of claim 3 whereinsaid complex viscosity is from about 1.0×10⁵ to 100.0×10⁵ poise.
 5. Aresin of claim 4 wherein said complex viscosity is from about 4.0×10⁵ toabout 60.0×10⁵ poise.
 6. A resin of claim 2 wherein said resin particlesare characterized by having:(a) a shape factor less than about 0.83; (b)a mercury porosity of from about 0.3 cc/g to about 0.5 cc/g; (c) aparticle size of from about 100 microns to about 250 microns; (d) afriability of less than about 1; (e) a powder mix time less than about300 seconds; and (f) greater than about 50% of the surface area of saidparticle is PVC.
 7. A resin of claim 6 wherein said shape factor is lessthan about 0.80.
 8. A resin of claim 6 wherein said friability is about0.
 9. A resin of claim 6 wherein said powder mix time is less than about250 seconds.
 10. A resin of claim 6 wherein greater than about 60% ofthe surface area of said particles is PVC.
 11. A resin of claim 1wherein the surface of said resin particles are free of surfactants anddispersants.